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Song X.P.,University of Science and Technology Beijing | Cheng S.S.,University of Science and Technology Beijing | Cheng Z.J.,University of Science and Technology Beijing | Cheng Z.J.,Jiuquan Iron and Steel Group Co.
Ironmaking and Steelmaking | Year: 2013

A three-dimensional unsteady coupled mathematical model has been applied to analyse the turbulent flow, temperature fields and macroscopic solidification of molten steel in billet continuous casting with electromagnetic stirring (EMS). Induction currents caused by fluid flow and the stirrer end effect have been investigated. The Lorentz force and Joule heat caused by induction currents have also been taken into account. The application of EMS in the secondary cooling zone results in significant changes in molten steel flow and temperature distribution, and the flow patterns on the horizontal cross-section agree well with the results in other references. Joule heat and Lorentz force are mainly located at the surface layer of the billet and decrease rapidly with penetration depth. The degree of superheat is reduced or eliminated rapidly when molten steel is stirred by EMS, hence is beneficial to generate more equiaxed grains. Stirring intensity is highest in the regions near the two ends of the stirrer. The Joule heat produced by induction has limited influence and can be ignored. The industrial trials showed that the EMS can effectively suppress the central shrinkage cavity and the centre C segregation to improve product quality. © 2013 Institute of Materials, Minerals and Mining. Source

Song X.,University of Science and Technology Beijing | Cheng S.,University of Science and Technology Beijing | Cheng Z.,University of Science and Technology Beijing | Cheng Z.,Jiuquan Iron and Steel Group Co.
ISIJ International | Year: 2012

Steady molten steel flow in CSP (Compact Strip Production) thin slab mold has been calculated via numerical simulation with heat transfer and solidification considered, and then the trajectories of inclusions have been calculated based on the flow field simulated. The solidifying shell has great influence on fluid flow and heat transfer in thin slab CSP mold, thus it should not be neglected while investigating the inclusion metallurgical behavior. The influence of solidifying shell on inclusion behavior has been particularly evaluated. Because the complex and irregular geometry of solidification front, grid of solidification front in mold has been used to judge whether inclusion is absorbed. Through the trajectories of inclusions, a statistics method to study the motion and distribution of inclusions by the "collision event" between inclusions and sampling surfaces has been used. The influence of inclusion diameter, density and casting speed on inclusion removal, also inclusion distribution within the solidifying shell in mold have been evaluated using this method. It is concluded that the distribution of inclusions in solidifying shell is not well-proportioned mainly due to fluid flow pattern in mold, diameter of inclusion, density of inclusion and casting speed. The ratio of inclusion floating to free surface decreases with casting speed rising, and the time for inclusions to float to free surface gets shorter. Inclusions with larger diameter are more possible to be frozen in solidifying shell with shallow skin depth. Removal of inclusions with smaller diameter is not sensitive to the above factors. © 2012 ISIJ. Source

Jing G.,University of Science and Technology Beijing | Shu-Sen C.,University of Science and Technology Beijing | Zi-Jian C.,University of Science and Technology Beijing | Zi-Jian C.,Jiuquan Iron and Steel Group Co.
ISIJ International | Year: 2013

The formation and modification of non-metallic inclusions for Al-killed steel during Compact Strip Production Process (CSP Process) was studied by industrial experiments. The thermodynamics for the formation of Al 2O3, MgO·Al2O3 spinel, various calcium aluminates and CaS bearing inclusion were analyzed with the help of calculation software FactSage. It is found that the oxygen activity in liquid steel during LF (Ladle Furnace) refining is confirmed to be determined by the equilibrium between dissolved Al and Al2O3 in inclusion. There are two manners for Al2O3 inclusion modification during LF refining: the first route is followed by Al 2O3-low modified calcium aluminates-liquid calcium aluminates; and the other is as Al2O3- MgO·Al 2O3 spinel-CaO-MgO-Al2O3 multi-component inclusion. In addition, the liquid calcium aluminates have the tendency to be multi-component inclusion. Two types of CaS bearing inclusion could precipitate in a slab during solidification. The favorable modified inclusions deform very well along with steel matrix during rolling process even if they are associated with CaS bearing layer, while the no or low modified Al2O3 based inclusion would be rolled into pieces and the micro-cracks might be generated around the inclusions. © 2013 ISIJ. Source

Cheng Z.-J.,University of Science and Technology Beijing | Cheng Z.-J.,Jiuquan Iron and Steel Group Co. | Guo J.,University of Science and Technology Beijing | Cheng S.-S.,University of Science and Technology Beijing
Kang T'ieh/Iron and Steel | Year: 2012

The reasonable content of MgO in refining slag calculated by the thermodynamic calculation software FactSage ranges from 4% to 8%, in which 6% is the best. In addition, slag-steel equilibrium at 1873 K between SiO 2-CaO-Al 2O 3-6%MgO quasi-ternary slag and liquid steel were analyzed on the basis of results of industrial sampling combined that calculated by FactSage both in liquid region and solid-liquid coexisting region with CaO saturation. It indicates that the refining slag with high basicity and high w(CaO)/w(Al 2O 3) (C/A) is favorable for control of low oxygen, low sulfur and low silicon. However, slag with too much CaO is disadvantageous of deoxidation and desiliconization that suggests refining slag is not the whiter the better as the supersaturated CaO do not take part in the slag-steel reaction and even worsen its kinetic conditions. Furthermore, the optimized compositions of refining slag in LF for SPCC in Jiuquan Iron and Steel Corporation (JISCO) are: CaO 50%-55%, Al 2O 3 30%-36%, SiO 2 1%-6%, MgO 4%-8% and 6% is best, basicity 9.0-14.0 and w(CaO)/w(Al 2O 3) is 1.5-1.8. Finally, both slag-steel equilibrium experiments in laboratory scale and industrial trials in plant scale verified that optimized slag has a better ability for deoxidation, desulfurization and control of silicon content, and could better control inclusion composition as well as its removal. Source

Guo J.,University of Science and Technology Beijing | Cheng S.,University of Science and Technology Beijing | Cheng Z.,University of Science and Technology Beijing | Cheng Z.,Jiuquan Iron and Steel Group Co. | Xin L.,University of Science and Technology Beijing
Steel Research International | Year: 2013

Thermodynamics for CaS bearing inclusions precipitation and their deformative behaviors during compact strip production (CSP) rolling process for Al-killed calcium treatment steel were researched using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) combined with the results of industrial trials. In addition, thermodynamic software FactSage was applied to calculate component activities of an inclusion and to analyze properties of sulfide-oxide duplex inclusions. It is possible for CaS bearing inclusion precipitation during secondary refining and continuous casting in two manners: the first is that Ca and S react directly after calcium treatment; the other is as the well modified calcium aluminates react with dissolved sulfur and aluminum in liquid steel. Correspondingly, two types of sulfide-oxide duplex inclusion were observed in casting slab. For the first type duplex inclusion, nearly no chemical reactions occur between outer CaS layer and solid inclusion core, thus the outer CaS rich layer is easily separated even taken off from the inner core during rolling process, and a crack may be generated correspondingly. The later one performs a better deformation during rolling process. The first type of duplex CaS bearing inclusion forms due to CaS precipitating directly surrounding solid inclusion core; the second type is as modified calcium aluminates react with dissolved sulfur and aluminum. During rolling, the outer CaS rich layer of the first type inclusion is easily separated from the inner core while the later one performs a better deformation. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

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